From Crystallites to Columns: Hierarchical Zn/Ni Bimetallic MOF-Biopolymer Composite Beads as High-Capacity Adsorbents for 17β-Estradiol in Water

• Facile synthesis of Zn-based CALF-20 MOF exhibiting multi-scale hierarchical architecture characterized by multi-model SAXS analysis. • Exceptional adsorption performance toward Bisphenol-A (329.3 mg g⁻¹) and 17-α Ethinylestradiol (392.93 mg g⁻¹), surpassing many reported MOFs. • Adsorption behavior follows Langmuir isotherm and pseudo-second-order kinetics, indicating monolayer adsorption and high binding affinity. • Hydrogen bonding, π–π interactions, and Zn–O coordination identified as dominant adsorption mechanisms through combined XPS and DFT analysis. • High stability, selectivity, and reusability establish CALF-20 as a promising MOF for sustainable removal of endocrine-disrupting contaminants from water. 17β-Estradiol (E2) is a potent endocrine-disrupting chemical (EDC) that exists in aquatic environments and poses serious risks to human and ecological health. In this study, we synthesized a Zn/Ni bimetallic metal–organic framework (MOF) using a continuous-flow reactor and embedded it within a κ-carrageenan/NH 4 A matrix to prepare composite beads for efficient E2 removal from water. The anisotropic MOF crystallites exhibited a hierarchical structure and assembled into the lamellar superstructures, forming accessible adsorption sites. Small angle x-ray scattering analysis showed a radius of gyration parameter of R g = 13.6 nm, providing an estimate of crystallite size. X-ray photoelectron spectroscopy (XPS) further confirmed the bimetallic surface composition of the Zn/Ni MOF. Batch adsorption experiments were performed to evaluate the effects of adsorbent dosage, initial E2 concentration, and solution pH. Under optimized conditions, the composite beads achieved 99.2% E2 removal with an adsorption capacity of 409.3 mg g −1 . Fixed-bed column studies further showed that the Thomas model satisfactorily described the breakthrough behavior, with a maximum column capacity of 623.82 mg g −1 at a flow rate of 2 mL min −1 , influent concentration of 40 mg L −1 , and bed height of 20 cm. Molecular dynamics simulations further supported the strong and stable interaction of E2 with the Zn/Ni MOF framework. These results demonstrate that Zn/Ni MOF@κ-car/NH 4 A is an efficient, robust, and sustainable adsorbent for removing steroidal estrogens from aqueous systems.